Making the world a better place, one line of code at a time

On copy prevention in HTML, part 2

Posted on Monday, April 16, 2007, at 9:49:00 PM UTC

The methods discussed in my previous post are crude and ugly. Most of the time, they do work, but they do nothing to prevent the user from viewing the source and copying the text from there. Also, the user has a right to select text that should not be denied. For example, if one wants to show someone part of a large document, the easiest way to do that is to select the part.

These texts were generated by a script (currently unavailable). It can do two things: Inflate (the first paragraph above) and Scramble (the second paragraph).

Using the Inflate option will add random characters in SPANs positioned absolutely between nine and ten thousand pixels to the left. When the user selects text, the random characters will also be selected, and when the text is copied, they will also be copied. It will randomly add up to five letters between every two characters, and it will ignore text in TEXTAREAs, SCRIPTs, and SELECTs.
Such text could be "deflated" by copying the source, then removing all text that matches the regular expression/<span[a-z0-9 ;:="']*?>[A-Za-z]</span>/
, removing all SPAN tags that contain a letter and an attribute. Therefore, I put each original letter in a very similar SPAN tag, complete with a random location, and gave both types of spans position:absolute and position:static, in different orders. This could also be matched by a regular expression, but it would be much more complicated, and I will not list it here. It would also be possible to write a GreaseMonkey script that would loop through the SPANs and delete all of them which has a position attribute equal to absolute. However, it would probably be easier to retype it manually.

Using the Scramble option will put each letter in to a SPAN, position them absolutely at their correct location, and randomize the order. Therefore, when the user selects the text, the selection will be scrambled, and when it is pasted, it will show up as nonsense. Spaces are rendered pointless by the procedure, and are therefore removed. Scrambled text will not select cleanly, but is nearly impossible to descramble. It would be possible to write a GreaseMonkey script that would sort the SPANs by top, then by left, but it would be much easier to retype the text manually.

When using this approach, remember to position the text's container, or it will show up in unexpected places. In addition, this approach will completely break word wrap,and must therefore be placed in a container with a fixed width. This width should be entered in the Width textbox in the scrambler so that the text will flow correctly.

These methods will definitely prevent all but the most determined and technically skilled copiers. However, they do not prevent OCR screenreaders. This will be discussed in part 3.